A conventional non-step type automatic transmission (hereinafter, referred as a CVT) for a vehicle is disclosed in Japanese Patent Application Laid-Open No. 63-57953 (1988), in which the gear ratio of the CVT is controlled so as to match a target gear ratio obtained by using a vehicle speed and a throttle opening. However, it was difficult to smoothly traverse the uphill or downhill.
Further, a control apparatus for the CVT of the vehicle is disclosed in Japanese Patent Application Laid-Open No. 63-121537 (1988), in which the performance of an engine brake and that of acceleration are improved such that it can be easy for a vehicle to run a road with gradient. In the control apparatus for the non-step type automatic transmission for the vehicle disclosed in Japanese Patent Application Laid-Open No. 63-121537 (1988), a target gear ratio of the CVT calculated by using a vehicle speed detected by a driven shaft rotation sensor and an opening of a throttle valve detected by a throttle valve opening sensor is corrected appropriately by using a correction amount of a speed ratio determined by an angle of inclination of the vehicle detected sequentially by a vehicle inclination angle sensor. Accordingly, since a value suitable for the road gradient can be set as the target speed ratio for the CVT, an effective engine brake can be automatically applied on the downhill and effective acceleration can be automatically obtained on the uphill. In other words, if this control apparatus is installed in a vehicle, both the running safety and performance can be obtained.
However, it is required to mount the vehicle gradient angle sensor on the vehicle in order to detect the road gradient. Accordingly, the manufacturing cost for the vehicle increases due to the attachment of new parts.